A box contains $4$ red marbles, $3$ green marbles, and $6$ blue marbles. If a marble is randomly chosen, what is the probability that it is not red?
Solution: There are $4 + 3 + 6 = 13$ marbles in the box. There are $4$ red marbles. That means $13 - 4 = 9$ are not red. The probability is $ \frac{9}{13}$.